This invention relates to guidewires used in the placement of catheters in cardiovascular surgical procedures. More particularly, this invention relates to improvements in small diameter steerable guidewires.
A wide variety of guidewires are used for various medical purposes in the treatment of the human body. Among the more common uses is in blood vessels to guide a catheter to a site within the patient's blood vessel to perform the procedure for which the catheter is adapted. For example, guidewires, particularly small diameter steerable guidewires, perform an important function in percutanious translumenal coronary angioplasty ("PTCA").
Ideally, a guidewire should exhibit the following characteristics:
(1) a strong yet flexible tip; PA1 (2) an easily formable tip, although not so formable that the guidewire takes a permanent set when the wire is bent over on itself during use in the body; and PA1 (3) a tip that exhibits 1:1 tip torque response with no whipping.
Illustrative of such guidewires are those described in U.S. Pat. No. 4,545,390 to Leary and U.S. Pat. No. 4,538,622 to Samson et al. Each of the guidewires described in those patents has a tortionally rigid longitudinally flexible shaft and a flexible distal end that includes a radiopaque coil so that the physician can monitor fluoroscopically the position and advancement of the guidewire in the patient's blood vessel.
Many such existing guidewires provide a strong, flexible and formable tip. However, due to a non-symmetrical tip design including a flattened safety wire, such guidewires do not transmit torque 1:1. Where a guidewire does not provide 1:1 tip torque response, torsional energy is stored in the guidewire. At some point during arterial insertion the energy may be released causing the guidewire tip to "whip" or move in an unpredictable and uncontrolled manner. For a physician attempting to insert a guidewire in a tortuous anatomy, such unpredictable and uncontrolled behavior is unacceptable.
Accordingly, there is a need for a guidewire with a strong flexible tip that exhibits 1:1 tip torque response with no whipping.